The present invention relates to apparatus for accumulating stacks of note books, pads, pamphlets or analogous commodities including overlapping sheets which consist of paper or the like. More particularly, the invention relates to apparatus for stacking groups of sheets (hereinafter called pads for short) which issue from a producing or processing machine in a predetermined orientation, e.g., with their backs facing forwardly or backwards. Still more particularly, the invention relates to improvements in apparatus for stacking pads or like substantially flat commodities whose thickness is not uniform throughout so that, in the absence of remedial measures, the height of a stack would vary from one side to the opposite side of the stack.
It is known to deliver a file of pads in identical orientation to a stacking platform or table whereon successive pads are piled up on top of each other to form stacks of desired height. It is also known to equip such apparatus with stop means for arresting successive pads in a predetermined position in order to insure that each next-following pad will fully overlap the preceding pad. Fully grown stacks are transferred to a packing station or undergo further processing, for example, in a heating tunnel subsequent to introduction into envelopes consisting of shrinkable synthetic plastic material which contracts in response to the application of heat and tightly surrounds the respective stack.
The just described mode of stacking pads or the like is satisfactory as long as the thickness of each pad is constant throughout. In many instances, the thickness of at least one marginal portion of a pad exceeds the thickness of other portions, e.g., because the pad is assembled of folded sheets whose backs overlie or are placed into each other. Furthermore, the means for bonding or otherwise securing the leaves of pads to each other often or invariably contributes to greater thickness of the corresponding portion of the pad. This applies regardless of whether the sheets or leaves are held together by staples, stitches or, as in the case of certain types of steno pads, by helical or otherwise configured binders made of helically convoluted or comb-shaped metallic or plastic wire. The accumulation of a relatively small number of such pads on top of each other results in the formation of a stack whose upper surface slopes from one marginal zone toward the opposite marginal zone. Therefore, the maximum permissible height of such stacks is relatively small and the wrapping of stacks in heat-shrinkable plastic material or packing of stacks in crates, boxes or other types of containers presents many problems. A certain height cannot be exceeded because the pads of a stack are likely to overturn which can cause lengthy delays and contributes to a pronounced reduction of the output of an automatic or semiautomatic stacking apparatus.
Attempts to overcome the just discussed problems in connection with the stacking of pads of varying thickness include the accumulation of relatively small stacks and the placing of two small stacks on top of each other so that the thicker portions of pads which form one of the small stacks are adjacent to one side and the thicker portions of pads constituting the other small stack are adjacent to the opposite side of the resulting composite (higher) stack. Such procedure is acceptable when the thickness of one marginal portion of each pad exceeds only slightly the thickness of the remaining major portion of the same pad. However, the just discussed procedure is not acceptable when the leaves of pads are held together by binders whose diameters often greatly exceed the thickness of the respective pile of sheets. The accumulation of relatively low stacks wherein the binders are superimposed upon each other can result in pronounced instability of the stack and the convolutions or prongs of neighboring binders are likely to become interlaced to thus prevent orderly removal of pads from stacks. Therefore, pads wherein the leaves are held together by spirals or otherwise configurated binders are normally stacked by hand. Such mode of stacking is costly and time-consuming. Moreover, it is difficult to stack the pads by hand at the same rate at which they issue from a high-speed automatic or semiautomatic machine wherein the leaves of pads are connected to each other by spirals or otherwise configurated binders.